Portable resource modules comprising electronic data stores and program stores as well as one or more processors are known and are designed conventionally with interfaces for removable connection to a host device. Via this removable connection, a portable resource module and a host device can be hooked up for temporary interaction and co-operation. The host device can access data stores in the portable resource module, for example, or co-operate with a software application, which is executed on a processor of the portable resource module. The known portable resource modules are typically designed in the form of so-called chipcards, but they can also be designed differently, for instance as so-called electronic tokens. Among the most well known chipcards are the SIM cards (Subscriber Identity Module), which is removably connectible to a mobile radio telephone as an identification and authentication module, and the bancomat card which is removably connectible to bancomats or so-called ATMs (Automatic Teller Machines). Along with the progress in miniaturisation of electronic components, the memory capacity and the processor capacity of portable resource modules have been continuously enlarged, so that it has become realistic to use the resource modules not merely for a dedicated application but for a plurality of applications. In particular, in connection with communication terminals, with networked host devices and with suitable writing devices, it has become possible moreover for authorised parties to transmit additional software applications dynamically onto the portable resource modules, store them there, and execute them on the local processor. Increased security problems have thereby arisen, however, since the possibility has existed that additionally loaded software applications could access data of other software applications in the portable resource module in an unauthorised way.
Described in the patent application EP 0 908 855 is a resource control mechanism for chipcards having a plurality of software applications, which mechanism makes available resources for the software applications in the chipcard and prevents data of other software applications in the card from being accessed in an unauthorised way. If the chipcard is connected to a host device, the resource control mechanism according to EP 0 908 855 makes it possible to receive requests from the host device for the execution of the software applications, to provide, by means of a memory area table stored in the chipcard, a memory area for the storage and for the execution (inclusive data storage) of a respective software application as resources and to check that the respective software application is executed in the resources made ready therefor. The resource control mechanism according to EP 0 908 855, however, cannot prevent redundant, i.e. already available, software applications from being loaded onto the chipcard or unnecessary loading attempts from being made for additional software applications when no resources therefor are available on the chipcard. This is a drawback in particular if software applications are supposed to be loaded onto a multiplicity of resource modules via a communication network since network and storage capacity are thereby wasted unnecessarily.